1. Field of the Invention
The present invention relates to a resist pattern forming method suitably usable in the ultramicrolithography process such as production of VLSI or a high-capacity microchip as well as in other photofabrication processes and capable of forming a highly defined pattern by using an electron beam (EB) or an extreme-ultraviolet ray (EUV), a resist pattern, a positive resist composition, a nanoimprint mold and a photomask. More specifically, the present invention relates to a resist pattern forming method for use in the process where a substrate with a specific underlying film is used, a resist pattern, a positive resist composition, a nanoimprint mold and a photomask.
The resist pattern forming method of the present invention can be also suitably used for the production method of a nanoimprint mold structure.
2. Description of the Related Art
In the microfabrication using a resist composition, with an increase in the integration degree of an integrated circuit, formation of an ultrafine pattern (for example, a 1:1 line-and-space pattern with a line width of 30 nm or less, that is, a repetition of lines of 30 nm or less and spaces of 30 nm or less) is recently required.
To meet this requirement, the exposure wavelength tends to become shorter, such as from g line to i line or further to excimer laser light and at present, development of a lithography technique using an extremely-ultraviolet light (EUV) or an electron beam is proceeding. In recent years, the resist composition is also used for an application to produce a mold for use in the so-called imprint process (for example, JP-A-2008-162101 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) and Yoshihiko Hirai (compiler), Nanoimprint no Kiso to Gijutsu Kaihatsu•Oyo Tenkai—Nanoimprint no Kiban Gijutsu to Saishin no Gijutsu Tenkai (Basic and Technology Development•Application Expansion of Nanoimprint—Base Technology of Nanoimprint and Latest Technology Expansion), Frontier Shuppan (issued on June, 2006)).
Furthermore, the progress in refinement of a pattern formed brings about a new problem of pattern collapse and in order to solve this problem, thinning of the resist film is being applied in combination.
As for the lithography technology using an extreme-ultraviolet light (EUV) or an electron beam or as for the resist composition used for an application to produce an imprint mold, those using a resin in which a hydrogen atom of a phenolic hydroxyl group is replaced by an acid-labile group such as acetal structure are disclosed in JP-A-2000-239538, JP-A-2006-146242 and International Publication No. 05/023880.
An aqueous 2.38 mass % tetramethylammonium hydroxide solution (hereinafter simply referred to as an aqueous TMAH solution) is in fact used as a standard developer in industry, but the above-described thinning of a resist film raises a problem such as disconnection of patterns and LER performance deterioration due to film loss of the resist film during development.
In order to solve this problem, there have been proposed, for example, a method where when developing a positive novolak resist, the pattern is developed with a 0.115 N to 0.15 N alkali developer (JP-A-63-232430), and a method where a resist film formed of a resist composition containing a resin having an ester-type acid-decomposable repeating unit is developed using an aqueous TMAH solution with a concentration of 1.2 mass % or less (JP-A-2010-134240).